Plan for the next three months

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15 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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1

Plan for the next three months

Shinji Machida

ASTeC/STFC/RAL

16 December 2010

2

Main tasks


Acceleration/deceleration needs the following
tasks


Phase adjustment of individual cavity (longitudinal).


Orbit correction (transverse).


Attempt at extraction (if possible).



Hopefully all the BPM (42 between QD and QF)
will be ready by January 2011.

3

Phase adjustment of individual cavity

4

Possible methods


Without beam


Relative phase between LLRF and monitor port.


With beam


Beam loading signal at monitor port.


Horizontal displacement at BPM.


Synchrotron oscillation amplitude and frequency.



With and without cavity detuning

5

Request and assumption


An issue of “random new angle after a sweep”
must be resolved before any beam based
measurements.

6

Beam loading signal at monitor port (1)


This is done with multiple turns only.


No need to detune other cavities.


Phase slippage (questioned by Jamison) may
not be a problem because cavity is tuned to
revolution frequency (and self bunching).



Accuracy is not clear.

7

Beam loading signal at monitor port (2)


Can be improved if we can choose a shot
with similar number of turns.



Is it possible to take beam loading signal and
BPM signal of the same shot through EPICS?

8

Horizontal displacement at BPM (1)


A beam is deflected by different angle with
different momentum.


Dispersion function tells a rough estimate.



e.g. 120 kV energy gain at a cavity




dispersion function of 60 mm





All the cavity except one has to be detuned.

9

Horizontal displacement at BPM (2)


Betatron oscillation is excited at cavity #4
because of a sudden jump of equilibrium orbit.


Osc. amplitude is ~0.7 mm (full) with 120 kV.



Red:

+120 kV

Green:


0 V

Blue:


-
120 kV

cavity #4

10

Horizontal displacement at BPM (3)


In reality, injection error excites another betatron
oscillation at the beginning.


Have to measure small difference.

Red:

+120 kV

Green:


0 V

Blue:


-
120 kV

11

Horizontal displacement at BPM (4)


Multiple passage gives more energy gain and
larger displacement.


This is nothing but synchrotron oscillation
observed through dispersion function.

Red:

+120 kV

Green:


0 V

Blue:


-
120 kV

100 turns

0 turns

12

Synchrotron oscillation (1)


Assume that all the cavity except one is
detuned.


Synchrotron oscillation
amplitude

depends on
the initial phase.

Initial phase


Red:


270 deg.


Green: 340 deg.


Blue:


350 deg.

13

Synchrotron oscillation (2)


When vector sum becomes the maximum, it
gives the maximum synchrotron oscillation
frequency
.


No need to detune cavities.


Maximize synchrotron frequency by sweeping
individual cavity phase.



Simulation is in progress.

14

Plan for phase adjustment


My preference of “with beam” measurement is
the following order.


Beam loading measurement synchronized with BPM
signal.


Synchrotron
frequency

measurement.




both do not need detuning



Synchrotron
amplitude

measurement.


Measurement of displacement at BPM.




need detuning

15

Orbit correction

16

horizontal

vertical

Source of COD (1)


Assume the observed COD comes only from
misalignment of QD (red) and QF (green).


It needs rather large misalignment.

17

Source of COD (2)


Vertical corrector is suspicious although a
simple model with different integrated
gradient was not enough to explain the COD.


Field calculation has been done (Shepherd.)






More detailed simulation including field
distribution has not finished yet.

18

Source of COD (3)


QF41 shifted longitudinally by 6.5 mm.


This could be a source although simple hard edge
model was not enough to explain the COD.


Field calculation has been done (Giboudot.)



More detailed simulation including field
distribution has not been done yet.

19

Correction (1)


Setup a model lattice which has a similar
COD in vertical direction.


Use vertical misalignment of 84 quadrupoles.

Red cross: observed COD

Green: COD reconstructed

20

Correction (2)


Correct COD by SVD using 16 V
-
corrector.


Decelerate in serpentine channel.

Green: before correction

Red: after correction

COD

Tracking results

21

Correction (3)


Identify tune where beam amplitude grows.

Green: before correction

Red: after correction

Red:
horizontal tune

Greed: vertical tune

Tracking results

deceleration

Qz=8

7 6 5

22

Correction (4)


Harmonic analysis before and after COD
correction with SVD.

Green: before correction

Red: after correction

COD

23

Correction (5)


COD after removing harmonic of 8.

Green: all harmonics

Red: after removing h=8

COD

24

Correction (6)


Amplitude growth is suppressed after
removing h=8.

Green: all harmonics

Red: after removing h=8

COD

Tracking results

25

Correction (7)


Tracking simulation shows eliminating one
harmonic component is more effective than
reducing orbit deviation on average by SVD.



Eliminating harmonic component of integer
part of tune (4 to 11 for vertical) seems to be
a way of orbit correction in a linear nonscaling
FFAG.

26

Possible explanation


If a lattice has harmonic of
n
, integer tune of
n

becomes systematic resonance.


Tune change per periodic unit decreases by a
factor of 42/
n
. For example, with harmonic of
n
=8, crossing speed becomes one order
lower.


With harmonic of
n
, it is equivalent to have
n

times smaller ring with
n

times more turns.




27

Plan for orbit correction


Measure COD at several different momenta
to identify error source or harmonics of errors
at least.



Apply harmonic correction.



If necessary, move some of quadrupole
magnets vertically.